Information recording apparatus and information recording method

ABSTRACT

In the information recording apparatus, by driving the light source by the pulse signal corresponding to the recording signal, the laser pulse corresponding to the recording signal is irradiated onto the recording medium. The recording signal has the mark period to form the recording mark, and the space period in which the recording mark is not formed. In the mark period, the output level of the laser pulse changes between the normal level and the writing level, thereby, the recording mark is formed on the recording medium. On the one hand, over a predetermined period in the space period, the output level of the laser pulse is changed to the low level lower than the normal level. Thereby, the heat accumulation onto the recording medium, due to the transient response of the laser pulse in the mark period, is reduced, and in the mark period after that, the correct recording mark can be formed.

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to the subject matter contained inJapanese Patent Application No.2001-266460 filed on Sep. 03, 2001, whichis incorporated herein by reference in its entirety.

[0002] The present invention belongs to a technology to record theinformation onto the optical disk by using the laser light beam.

[0003] The laser light is irradiated onto the recording surface of thedisk and the information is recorded in the writable or re-writableoptical disk such as DVD-R (DVD-Recordable) or DVD-RW(DVD-Re-recordable) . At a portion onto which the laser light isirradiated, on the recording surface of the optical disk, because thetemperature rises, a change is generated in the optical recording mediumconstituting the optical disk, thereby, a recording mark is formed onthe recording surface.

[0004] Accordingly, by the recording pulse having the time widthcorresponding to the information to be recorded, the laser light ismodulated, and the laser pulse having the length corresponding to thesignal to be recorded is generated, and by irradiating this onto theoptical disk, the recording mark having the length corresponding to theinformation to be recorded, can be formed on the optical disk.

[0005] On the one hand, recently, one recording mark is not formed bythe one laser pulse, and a method by which the recording mark is formedby the pulse train including a plurality of short pulses, is used. Sucha method is also called write strategy, and as compared to a method bywhich a single recording pulse is irradiated, because the heataccumulation on the recording surface of the optical disk is reduced,the temperature distribution on the recording surface on which therecording mark is formed can be uniformed. As the result, it isprevented that the recording mark becomes the tear drop shape, and thepreferably shaped recording mark can be formed.

[0006] The above recording pulse train is structured by a plurality ofpulses whose amplitude is varied between a predetermined read powerlevel and write power level. That is, according to the recording signal,in the area on the recording surface of the optical disk (hereinafter,called also “space portion”) in which the recording mark is not formed,the laser light is irradiated onto the recording surface by the readpower, and in the area on the recording surface of the optical disk(hereinafter, called also “mark portion”) in which the recording mark isto be formed, the laser light is irradiated onto the recording surfaceby the power corresponding to the recording pulse train whose amplitudeis varied between the read power and the write power, thereby, therecording mark is formed on the recording surface.

[0007] However, when the laser pulse corresponding to the recordingpulse is irradiated onto the recording surface of the optical disk, bythe transient response of the pulse, the laser irradiation level (biaslevel) after the irradiation of the recording pulse is increased. Therecording pulse whose amplitude is varied between the read power andwrite power, and after the completion of the recording pulse,theoretically, the laser irradiation level instantaneously returns tothe read power. However, practically, at the time of completion of therecording pulse, because the laser irradiation level instantaneouslychanges from the write power to the read power, the transient responseof the recording pulse is generated, and the laser irradiation leveldoes not instantaneously return to the read. power, but rather than it,the laser irradiation level is increased for a constant period. As theresult, also after the recording pulse is completed, although it is ashort time, a period in which the laser irradiation level is higher thanthe read power level, is generated. There is a case where thisinfluences the formation of the next recording mark as the heatinterference. Particularly, when the space period to the next recordingmark is short, because there is the residual heat by the above transientresponse at the time of formation of the next recording mark, there is acase where the next recording mark can not be correctly formed.

[0008] Then, this influence is specifically prominent when the recordingspeed is increased, that is, when the high speed recording is conductedonto the optical disk. In the case of the recording of the normal speed(low speed), because a time period to the mark period corresponding tothe next recording mark can be secured to some extent, the influence ofthe above transient response is softened, however, when the recordingspeed is increased to 2 times or 3 times of the normal one, because thetime interval of the recording pulse train becomes short, the nextrecording pulse train comes under the condition that the residual heatis remained, and the possibility that the residual heat due to the abovetransient response influences the next recording mark as the heatinterference is increased.

[0009] Further, when the recording speed is increased, in order to formthe recording mark correctly, it is necessary that the recording poweris increased corresponding to the increased amount of the recordingspeed. Accordingly, the increase of the laser irradiation level becomeslarge, and the bad influence is increased.

[0010] Then, because the increase of the laser irradiation level due tothe transient response of the recording pulse is generated after theapplication of the recording pulse as described above, that is, in thespace period of the recording signal, this influence can not be removedby the write strategy technology by which the pulse width of therecording pulse is adjusted, and the recording mark shape is adjusted.

SUMMARY OF THE INVENTION

[0011] In view of the above problems, the present invention is attained,and the object of the present invention is to provide an informationrecording apparatus and the method by which, even at the time of thehigh speed recording, the influence of the transient response of therecording pulse train is eliminated and the correct recording mark canbe formed.

[0012] In one point of view of the present invention, in an informationrecording apparatus in which the laser light is irradiated onto therecording medium and a recording mark corresponding to a recordingsignal is formed, it is provided with: a light source to emit the laserlight; and a controller which controls to irradiate a laser pulse ontothe recording medium when the light source is driven according to therecording signal, and the controller is provided with: a mark controllerby which, during a mark period of the recording signal, the output levelof the laser pulse is changed corresponding to the recording signalbetween a normal level and a higher writing level than the normal level;and a space controller by which, during at least several space periodsin the recording signal, the output level of the laser pulse is changedto the low level lower than the normal level covering over apredetermined period.

[0013] According to the above information recording apparatus, when thelight source is driven corresponding to the recording signal, the laserpulse corresponding to the recording signal is irradiated onto therecording medium. The recording signal has the mark period to form therecording mark and the space period in which the recording mark is notformed. In the mark period, the output level of the laser pulse changesbetween the normal level and the writing level, thereby, the recordingmark is formed on the recording medium. On the one hand, over apredetermined period in the space periods, the output level of the laserpulse is changed to the low level lower than the normal level. Thereby,the heat accumulation onto the recording medium due to the transientresponse of the laser pulse in the mark period is reduced, and in themark period after that, the correct recording mark can be formed.

[0014] In one mode of the above information recording apparatus, the lowlevel lower than the normal level is a zero level.

[0015] According to this mode, in the space period, because the level ofthe laser pulse temporarily becomes zero, the accumulation of the heatto the recording medium is sufficiently reduced during that period.

[0016] In another mode of the above information recording apparatus, thespace controller changes the output level of the laser pulse to the lowlevel lower than the normal level only in the space period in which thetime width is short.

[0017] According to this mode, the output level of the laser pulse isreduced only in the space period in which the time width is short. Whenthe time width of the space period is short, while the heat on therecording medium by the laser pulse irradiated in the mark periodpreceding to that, is not sufficiently reduced, the next mark periodcomes and the probability in which the bad influence such as the heatinterference is given to the next recording mark formation, is large.Accordingly, even when the output level of the laser pulse is reducedonly in the space period in which the time width is short, good effectcan be obtained.

[0018] In yet another mode of the above information recording apparatus,the space period in which the time width is short can be the spaceperiod of 3T or 4T.

[0019] In yet another mode of the above information recording apparatus,the space controller changes the output level of the laser pulse to thelow level lower than the normal level in all space periods.

[0020] According to this mode, in all space periods, because the outputlevel of the laser pulse is reduced, the influence of the heatinterference due to the transient response of the laser pulse in themark period can be effectively eliminated.

[0021] In further yet another mode of the above information recordingapparatus, in the space period in which the time width is long, thespace controller changes the output level of the laser pulse to the lowlevel over the predetermined first period, and in the space period inwhich the time width is short, the output level of the laser pulse ischanged to low level over the second period which is longer than thefirst period.

[0022] According to this mode, in the short space period, because thetransient response of the laser pulse during the preceding mark periodeasily influences the next mark period, the output level of the laserpulse is lowered over the longer period.

[0023] In further yet another mode of the above information recordingapparatus, the space period in which the time width is short is a spaceperiod of 3T or 4T, and the space period in which the time width is longcan be a space period of 5T or more.

[0024] In further yet another mode of the above information recordingapparatus, it is further provided with a level adjuster whichautomatically adjusts the output level of the laser pulse over the leveladjustment period in the predetermined space period, and the spacecontroller changes the output level of the laser pulse to the low levellower than the normal level only in the space period in which the outputlevel is not automatically adjusted.

[0025] According to this mode, the output level of the laser pulse islowered only in the space period in which the output level of the laserpulse is not automatically adjusted.

[0026] In further yet another mode of the above information recordingapparatus, it is further provided with a level adjuster whichautomatically adjusts the output level of the laser pulse over the leveladjustment period in the predetermined space period, and the spacecontroller changes the output level of the laser pulse to the low levellower than the normal level in all space periods, in the period otherthan level adjustment period.

[0027] According to this mode, within the range which does not influencethe automatic adjustment of the output level of the laser pulse, theoutput level of the laser pulse can be lowered.

[0028] In further yet another mode of the above information recordingapparatus, it is further provided with a level adjuster whichautomatically adjusts the output level of the laser pulse over the leveladjustment period in the predetermined space period, and the spacecontroller changes the output level of the laser pulse to the low levelover the predetermined first period which does not overlap with thelevel adjustment period, in the space period in which the automaticadjustment of the output level is conducted, and in the space period inwhich the automatic adjustment of the output level is not conducted,over the second period longer than the first period, the output level ofthe laser pulse is changed to the low level.

[0029] According to this mode, in the space period in which theautomatic adjustment of the laser pulse is not conducted, the outputlevel of the laser pulse is lowered over a long period, and in the spaceperiod in which the automatic adjustment of the laser pulse isconducted, the output level of the laser pulse is lowered in the rangewhich does not influence the automatic adjustment.

[0030] In further yet another mode of the above information recordingapparatus, the recording medium is a recording medium in which therecording can be conducted only once, and the normal level can be areading level.

[0031] According to this mode, the present invention can be applied tothe recording medium such as CD-R or DVD-R.

[0032] In further yet another mode of the above information recordingapparatus, the recording medium is a recording medium in which thewiring and erasing can be conducted over a plurality of times, and thenormal level can be an erasing level.

[0033] According to this mode, the present invention can be applied tothe recording-medium such as CD-RW or DVD-RW.

[0034] In further yet another mode of the above information recordingapparatus, the space controller changes the output level of the laserpulse to the low level lower than the normal level from the top of thespace periods.

[0035] According to this mode, because the output level of the laserpulse is lowered from the top of the space periods, after the completionof the mark period in which the laser pulse of the writing level isirradiated, the laser power is lowered at once, and the influence of thetransient response can be effectively rejected.

[0036] In the another point of view of the present invention, in theinformation recording method in which the laser light is irradiated ontothe recording medium and the recording mark corresponding to therecording signal is formed, it has a step to emit the laser light and astep by which, by driving the light source according to the recordingsignal, the laser pulse is irradiated onto the recording medium, and thestep to emit the laser pulse has a step by which, during the mark periodof the recording signal, the output level of the laser pulse is changed,corresponding to the recording signal, between the normal level and thewriting-level higher than the normal level, and a step by which, duringat least several space periods of the recording signal, covering overthe predetermined period, the output level of the laser pulse is,changed to the low level lower than the normal level.

[0037] According to the information recording method, by driving thelight source by the pulse signal corresponding to the recording signal,the laser pulse corresponding to the recording signal is irradiated ontothe recording medium. The recording signal has the mark period to formthe recording mark, and the space period in which the formation of therecording mark is not conducted. In the mark period, the output level ofthe laser pulse changes between the normal level and the writing level,thereby, the recording mark is formed on the recording medium. On theother hand, over the predetermined period in the space period, theoutput level of the laser pulse is changed to the low level lower thanthe normal level. Thereby, the heat accumulation onto the recordingmedium due to the transient response of the laser pulse in the markperiod, is reduced, and in the mark period after that, the correctrecording mark can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a block diagram showing the outline structure of aninformation recording reproducing apparatus to which the presentinvention is applied.

[0039]FIG. 2 is a block diagram showing the structure of a recordingcontrol section shown in FIG. 1.

[0040]FIG. 3 is a view showing the structure of an LD driver shown inFIG. 2.

[0041]FIG. 4 is a graph showing the relationship between the drivecurrent given to a laser diode and the output power.

[0042]FIG. 5 is a timing chart showing a waveform of each portion of arecording control section at the time of the recording control accordingto the first embodiment of the present invention.

[0043]FIGS. 6A and 6B are waveform views showing a laser output levelincluding a laser off period.

[0044]FIGS. 7A to 7C are waveform views of a reading RF signal of arecording mark.

[0045]FIG. 8 is a timing chart showing the wave form of each portion ofthe recording control section at the time of the recording controlaccording to the second embodiment of the present invention.

[0046]FIG. 9 is a timing chart showing the wave form of each portion ofthe recording control section at the time of recording control accordingto the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Referring to the drawings, the preferred embodiment of thepresent invention will be described below.

[0048] (1) Apparatus Structure

[0049] In FIG. 1, the overall structure of an information recordingreproducing apparatus according to the embodiment of the presentinvention is generally shown. The information recording reproducingapparatus 1 records the information in an optical disk D, and reproducesthe information from the optical disk D. As the optical disk D, variousoptical disks such as, for example, CD-R (Compact Disc-Recordable),DVD-R in which the recording can be conducted only once, or CD-RW(Compact Disc-Rewritable), DVD-RW in which, over a plurality of times,the erasing and recording can be conducted, can be used.

[0050] The information recording reproducing apparatus 1 is providedwith: an optical pick-up 2 by which the recording beam and reproducingbeam are irradiated onto the optical disk D; a spindle motor 3 by whichthe rotation of the optical disk D is controlled; a recording controlsection 10 by which the recording of the information onto the optical Ddisk is controlled; a reproducing control section 20 by which thereproduction of the information which is already recorded in the opticaldisk is controlled; and a servo control section 30 by which each kind ofservo control including a spindle servo to control the rotation of thespindle motor 3, and a focus servo which is a relative position controlof the optical pick-up 2 to the optical disk D, and a tracking servo, isconducted.

[0051] The recording control section 10 receives the recording signal,and generates a drive signal S_(D) to drive the laser diode inside theoptical pick-up 2 by the processing which will be described later, andsupplies it to the optical pick-up, 2.

[0052] The reproducing control section 20 receives the reading RF signalSrf outputted from the optical pick-up 2, and a predetermineddemodulation processing and decoding processing are conducted on that,and the reproduction signal is generated and outputted.

[0053] The servo control section 30 receives the reading RF signal Srffrom the optical pick-up 2, and according to that, a servo signal S1such as the tracking error signal, and focus signal is supplied to theoptical pick-up 2, and the spindle servo signal S2 is supplied to thespindle motor 3. Thereby, each kind of servo processing such as thetracking servo, focus servo, or spindle servo, is conducted.

[0054] In this connection, the present invention mainly relates to therecording method in the recording control section 10, and for thereproducing control and servo control, because the already known variousmethods can be applied, for these methods, the detailed description isnot conducted.

[0055] Further, in FIG. 1, the information recording reproducingapparatus as one embodiment of the present invention is shown, however,the present invention can also be applied to the recording-onlyinformation recording apparatus.

[0056] In FIG. 2, the internal structure of the optical pick-up and therecording control section 10 are shown. As shown in FIG. 2, the opticalpick-up 2 is provided with: a laser diode LD which generates therecording beam to record the information to the optical disk D and thereproducing beam to reproduce the information from the optical disk D;and a front monitor diode (FMD) 16 which receives the laser lightemitted from the laser diode LD and outputs the laser power level signalLDout corresponding to the laser light.

[0057] In this connection, the optical pick-up 2 is provided with, otherthan that, already known components such as an optical detector toreceive the reflection beam by the optical disk D of the reproducingbeam and generate the reading RF signal Srf, and the optical system toguide the recording beam and reproduction beam, and reflection beam toan adequate direction, however, those illustrations and detaileddescription will be omitted.

[0058] On the one hand, the recording control section 10 is providedwith a laser diode (LD) driver 12, APC (Automatic Power Control) circuit13, sample hold (S/H) circuit 14, and controller 15.

[0059] The LD driver 12 supplies the current corresponding to therecording signal to the laser diode LD, and conducts the recording ofthe information onto the optical disk D. The front monitor diode 16 isarranged in the vicinity of the laser diode LD in the optical pick-up 2,receives the laser light emitted from the laser diode LD, and outputsthe laser power level signal LDout showing the level.

[0060] The sample hold circuit 14 samples the level of the laser powerlevel signal LDout at the timing regulated by the sample hold signalAPC-S/H, and holds it. The APC-circuit 13 power-controls the LD driver12 so that the read power level of the laser light emitted from thelaser diode LD becomes constant, according to the output signal of thesample hold circuit 14.

[0061] The controller 15 mainly conducts the recording operation and APCoperation. Initially, the recording operation will be described. In therecording operation, the controller 15 generates the switching signalSW_(R) and SW_(W) of the switch to control the current amount suppliedto the laser diode LD, and supplies it to the LD driver 12.

[0062] In FIG. 3, the detailed structure of the LD driver 12 is shown.As shown in FIG. 3, the LD driver 12 is provided with the current source17R for the read level, the current source 17W for the write level, andswitches 18R and 18w.

[0063] The current source 17R for the read level is the current sourcewhich flows the drive current I_(R) to make the laser diode LD emit thelaser light by the read power, and the drive current I_(R) is suppliedto the laser diode LD through the switch 18R. Accordingly, when theswitch 18R is turned on, the drive current I_(R) of the read power issupplied to the laser diode LD, and when the switch 18R is turned off,the supply of the drive current I_(R) is stopped. The magnitude of thecurrent from the current source 17R is changed by the control signalS_(APC).

[0064] The current source 17W for the write level is the current sourcewhich flows the drive current I_(W) to make the laser diode LD emit thelaser light by the write power, and the drive current I_(W) is suppliedto the laser diode LD through the switch 18W. Accordingly, when theswitch 18W is turned on, the drive current I_(W) of the write power issupplied to the laser diode LD, and when the switch 18W is turned off,the supply of the drive current I_(W) is stopped.

[0065] In FIG. 4, the relationship between the drive current supplied tothe laser diode LD, and the output power of the laser light which isemitted from the laser diode LD, is shown. As can be seen from FIG. 4,when the drive current I_(R) is supplied to the laser diode LD, thelaser light is emitted by the read power P_(R). Under that condition,when the drive current I_(W) is further added, the laser light isemitted by the write power P_(W).

[0066] At the time of recording of the information onto the opticaldisk, basically, the drive current I_(R) is always supplied, and thelaser light is emitted by the read power P_(R), and further, accordingto the recording pulse, by adding the drive current I_(W), the writepower P_(W) is applied, and the information is recorded onto the opticaldisk. However, in the present invention, as detailed below, it ischaracterized that: after the last pulse of the recording pulse train ofthe write power is applied, both of the switches 18R and 18W aretemporarily simultaneously turned off, and the drive current is madezero, thereby, the influence of the transient response is removed.

[0067] Next, the APC operation will be described. The APC operation isan operation by which the drive current level supplied from the LDdriver 12 to the laser diode LD is adjusted so that the level of theread power of the laser light outputted from the laser diode LD becomesconstant. In more detail, in the space portion of the recording signal(which is 8-16 modulated, and has the mark periods and space periods ofthe length of 3T-11T, 14T), in the long space period (for example, thespace period of 5T-11T, 14 T), the drive signal S_(D) from the LD driver12 is adjusted so that the level of the read power becomes constant.

[0068] Specifically, it operates as follows. The controller 15 generatesthe recording pulse corresponding to the recording signal as describedabove, and by the recording pulse, the LD driver 12 is driven and thelaser light is emitted from the laser diode LD.

[0069] The front monitor diode 16 is arranged in the vicinity of thelaser diode LD in the optical pick-up 2, receives the laser lightemitted from the laser diode LD, and the laser power level signal LDoutshowing the level is generated, and supplied to the sample hold circuit14.

[0070] The sample hold circuit 14 samples the laser power level signalLDout supplied from the front monitor diode 16, at the timing given bythe sample hold signal APC-S/H inputted from the controller 15, andholds its level for a predetermined period. The sample hold signalAPC-S/H outputted from the controller 15 is a pulse showing the periodin which the APC is conducted, and specifically, a pulse signal showinga predetermined period (the period in which the APC is conducted, andhereinafter, called also “APC period”) in the comparatively long spaceperiod in the recording signal (5T-11T).

[0071] Accordingly, the sample hold circuit 14 holds the level of thelaser power level signal LDout in the APC period in the space period ofthe recording signal and supplies it to the APC circuit 13. The APCcircuit 13 supplies the control signal S_(APC) to the LD driver 12 sothat the level of the laser power level signal LDout becomes constant inthe APC period.

[0072] The control signal S_(APC) is inputted into the current source17R for the read level in the LD driver 12 as shown in FIG. 3. Thereby,corresponding to the control signal S_(APC), the current I_(R) flowingfrom the current source 17R for the read level is changed. That is, theAPC is conducted so that the read power level obtained from the laserdiode LD becomes constant.

[0073] (2) (First Embodiment)

[0074] Next, referring to FIG. 5, the first embodiment of the recordingcontrol by the recording control section 10 will be described. FIG. 5 isa timing chart showing the waveform of each portion of the recordingcontrol section 10. In this connection, the first embodiment is anexample in which the recording control of the present invention isapplied to the recording of DVD-R.

[0075] In FIG. 5, the recording signal is a 8-16 modulation signal, andcorresponds to the mark to be formed on the recording surface of theoptical disk, and has the mark period and space period. On the recordingsurface of the optical disk, because a pit having any length of 3-11T,14T, is formed, in the recording signal, the mark period and spaceperiod of 3T-11T, 14T, are included. In the example of FIG. 5, in therecording signal, the mark period of the length 6T, space period of 5T,and mark period of 5T are shown.

[0076] The switching signal SW_(R) is a signal to switch the switch 18Rconnected to the current source 17R for the read power shown in FIG. 3,and as a principle, it is turned on in both of the mark period and spaceperiod. In the mark period, the switching signal SW_(W) to switch theswitch 18W connected to the current source 17W for the write power isswitched according to the recording pulse train. The recording pulsetrain is switched corresponding to a top pulse 120 whose time width islong, and the multi-pulse following that (called also “pulse train”)121. Then, in a predetermined period (period of the pulse 122) from thetiming at which the last pulse of the pulse train is completed, both ofthe switches 18R and 18W are turned off, and the current flowing thelaser diode LD is made zero.

[0077] In several periods after the last pulse of the pulse train iscompleted, as described above, due to the transient response of thepulse, the period in which the laser power level is higher than the readpower level is generated, however, as described above, in apredetermined period after the last pulse of the power train iscompleted, the read power is also turned off. (hereinafter, the periodis called “laser off period”), by making the current of the laser diodeLD zero, the increase of the laser power level generated due to thetransient response can be absorbed.

[0078] The waveform of the laser power level signal Lout shown in FIG. 5shows this situation. That is, in the mark period of the first 6T,initially, the read power P_(R) is continuously applied, and the toppulse 120 having the amplitude of the write power P_(W) and the pulsetrain 121 composed of 3 pulses are applied. Thereby, the recording markwhose length is 6T is formed on the recording surface of the opticaldisk.

[0079] Then, in the space period following the mark period of 6T, in thelaser off period 122 after the completion of the last pulse of the pulsetrain 121, not only the write power but the read power is also turnedoff, as the result, the laser power level signal LDout is lowered to thezero level LDoff. Then, when the laser off period 122 is completed, thelaser power level signal LDout is increased to the read power levelP_(R).

[0080] Also in the mark period of 5T of the right side in FIG. 5, in thesame manner, the laser off period 122 is provided (however, because of5T mark period, the pulse train 121 is composed of 2 pulses).

[0081] As described above, after the all mark periods are, completed,that is, when a predetermined laser off period is provided just afterthe last recording pulse in the mark period, the influence of transientresponse after the mark period completion can be removed.

[0082] The time width of the laser off period can be made changeable,and for example, it can be set to the arbitrary length between 1T-2T.However, in the time width of the laser off period, there is alimitation in the relationship with the APC. As described above, forexample, in the longer space period than 5T, the APC period is set, andthe laser power level signal LDout is sample-held by the sample holdcircuit 14, and because the APC is conducted so that the level ismaintained, it is necessary that, in the APC period, the laser powerlevel signal LDout is made to the read power level, and when the laseris turned off during the period, the hindrance occurs in the APC.

[0083] Accordingly, the laser off period 122 can not overlap with theAPC period (that is, the priod in which the sample hold signal APC-S/His in the low level) . Normally, the APC period is set in such a mannerthat the period of before or after 1-2T in the space period of 5T-11T isexcepted as a margin, and it is set in the remained period. Accordingly,in the margin of 1-2T in the top of the space period, even when thelaser is turned off, the hindrance does not occur in the APC. Therefore,in the space period in which the APC is conducted, it is preferablethat, in the laser off period, after the mark period is completed, it isset before the start of the APC period. Actually, as described above, itis preferable that, in the margin of 1T-2T provided in the top of thespace period, the laser off period is set.

[0084] In FIG. 6, an actual example of waveform of the laser light isshown. FIG. 6A is a waveform of the laser power level signal LDout whenthe laser off period is not provided, which is prepared for thecomparison, and FIG. 6B is the waveform of the laser power level signalLDout of the method (laser off period is provided) of the presentapplication. As shown in FIG. 6A, when the laser off period is notprovided, the transient response is generated after the last pulse ofthe pulse train, and the laser power level is increased (refer to aportion of code 130). In contrast to that, as shown in FIG. 6B, when thelaser off period is provided, the laser power level signal Ldout,temporarily drops to the zero level after the last pulse of the pulsetrain (refer to a portion of code 131). Accordingly, the residual heaton the recording surface of the optical disk is small, and the badinfluence due to the heat interference can be prevented from beingexerted onto the mark formation in the succeeding mark period.

[0085]FIG. 7 shows, when the laser off period is provided, and notprovided, the reading RF signal waveform of the recording markempirically formed on the optical disk. FIG. 7A is a case where thelaser off period is provided, and the envelope waveform of the readingRF signal of 3T mark, 4T mark, 5T mark, and 6T mark has a clear contour.

[0086] On the one hand, FIGS. 7B and 7C are envelope waveforms when thelaser off period is not provided, and the heat interference due to thetransient response of the pulse affects the succeeding mark formation.In the case of FIG. 7B, the contour of each envelope waveform is blurredand becomes bold, and in the case of FIG. 7C, further, it is seen as ifeach envelope wavelength is branched to two. Such the phenomenon iscaused by that the recording mark is inadequately deformed due to theheat interference.

[0087] As described above, according to the present invention, when thelaser off period is provided after the mark period, the influence of theheat interference due to the transient response of the recording pulseis excluded and the correct recording mark can be formed.

[0088] (3) (Second Embodiment)

[0089] Next, the second embodiment of the present invention will bedescribed. In the above first embodiment, the laser off period isprovided in the all space periods after the mark period, however, in thesecond embodiment, the laser off period is provided with only the shortperiod (for example, the space period of 3T or 4T), and the laser offperiod is not provided with the long space period (for example, thespace period more than 5T). In this connection, the second embodiment isalso an example in which the recording control of the present inventionis applied to the recording of the DVD-R.

[0090] The laser off period is provided for the purpose to remove theinfluence caused by that the laser power level is increased due to thetransient response after the completion of the recording pulse asdescribed above, however, when the space period following the markperiod is long, because there is the afford of time to the next markperiod, the transient response is hardly comparatively affected on thenext mark period. In contrast to this, when the space period followingthe mark period is short, because the time to the next mark period isshort, the probability that the residual heat of the level increasedamount due to the transient response exerts a bad influence on therecording mark formation in the next mark period, is increased.

[0091] From these reasons, even when the laser off period is provided inonly the short space period, the bad influence given to the markformation of the next mark period due to the transient response can beremoved.

[0092] In this case, the laser off period can be set longer than in thecase of the first embodiment. As described previously, in the long spaceperiod of 5T-11T, and 14T, the APC period to sample-hold the laser powerlevel signal LDout for the APC is set. Therefore, it is necessary thatthe laser off period is not overlapped with the APC period, and the timewidth of the laser off period is practically limited to the length ofabout 1T-2T.

[0093] In contrast to this, in the second embodiment, the laser offperiod is set only in the short space period (space period of 3T or 4T),and because the APC period is not set in the short space period, thelaser off period can be set long.

[0094] Referring to FIG. 8, this will be described. FIG. 8 shows thewaveform of each portion of the recording control section 10 in thesecond embodiment, and the space period of 3T exists after the markperiod of 6T, and further, the mark period of 5T follows. In the spaceperiod of 3T, because the APC period is not set, the sample hold signalAPC-S/H remains in the high level, and the sample-hold of the laserpower level signal LDout is not conducted. Accordingly, in the spaceperiod of 3T after the completion of the mark period of 6T, the laseroff period 122 is set sufficiently long. Thereby, the residual heat onthe information recording surface of the optical disk is reduced, andthe influence of the transient response of the recording pulse can beeffectively prevented from being exerted on the next mark period.

[0095] In this connection, in this meaning, it can also be said that thesecond embodiment is a method by which the laser off period is set onlyin the space period in which the APC is not conducted.

[0096] Further, the first embodiment and the second embodiment can becombined with each other. That is, as the first embodiment, the laseroff period is provided in all mark periods, and as the secondembodiment, in the short space period, the laser off period can be setlong. Thereby, in the case of the short space, because the laser offperiod becomes long, the heat interference can be effectively prevented.

[0097] (4) (Third Embodiment)

[0098] Next, the third embodiment of the present invention will bedescribed. The above first and second embodiments are examples in whichthe present invention is applied to the DVD-R, however, the thirdembodiment is an example in which the present invention is applied tothe DVD-RW. In FIG. 10, the waveform view of each portion of therecording control section 10 in the recording onto the DVD-RW is shown.In the DVD-RW, the recording mark is formed by basically the same methodas the DVD-R, however, because the erasing operation is conducted beforethe recording operation, as shown in the laser power level signal LDoutin FIG. 10, normally, the laser power from the laser diode LD is on theerasing level P_(E). Accordingly, the APC is also conducted when theerasing level P_(E) is sample-held in the APC period set in the longspace period.

[0099] In the same manner as in the case of the DVD-R, the recordingpulse train is structured by the top pulse 120 and the pulse train 121.Then, after the completion of the pulse train 121, the laser off period122 is provided, and the laser power level is temporarily dropped to thezero level LDoff. After that, the laser power level returns to theerasing level P_(E) which is steady state.

[0100] As described above, also in the case of the DVD-RW, when thelaser off period is provided after the completion of the recordingpulse, the influence of the heat interference due to the transientresponse can be removed.

[0101] In this connection, in the case of the DVD-RW, the time width ofthe laser off period is limited to the range by which the erasingoperation is not affected. That is, in the laser off period, because thelaser power level does not come to the erasing level, the erasing of theinformation already recorded on the DVD-RW cannot be conducted.Accordingly, when the laser off period is made too long, alreadyrecorded information can not be erased, and there is a disadvantage thatun-erased portion of the information is generated. Accordingly, the timewidth of the laser off period is limited to the comparatively shortperiod in which it does not affect the erasing of the information. Inthe practice, in the case of the DVD-RW, after the completion of therecording pulse, the period in which the laser power is dropped to theread level (it is called “cool pulse period”. Refer to the broken line140 in FIG. 9) is provided. Accordingly, as one preferred method, whenthe laser off period is provided in the cool pulse period, the problemsuch as un-erased portion is not generated.

[0102] (5) (Modified Example)

[0103] In the above laser off period, the current value given to thelaser diode LD is made zero so that the laser power level perfectlybecomes zero. However, even when the laser power level is not perfectlymade zero, when it is set to the low level lower than the read powerlevel, because the residual heat onto the disk is reduced by the amount,the effect by which the influence of the heat interference is reduced,can be obtained.

[0104] Further, in the above embodiment, the laser off period is startedafter the last pulse in the mark period is completed, however,theoretically, when it is before the next mark period comes, in anyportion in the space period, when the laser off period is provided, theheat interference with the next recording mark formation can be reduced.Particularly, in the space period in which the APC period is not set,because the laser off period with sufficient time width can be set, thelaser off period may not always start from just after the mark periodcompletion.

[0105] As described above, according to the present invention, in thespace period after the completion of the mark period, because the laseroff period in which the laser power is temporarily dropped to near thezero level is provided, the increase of the laser power level (biaslevel) due to the transient response of the recording pulse is softened,and the bad influence onto the next recording mark formation due to theheat interference can be prevented. This is effective in the point thatthe recording mark of the preferable shape can be formed particularlyeven in the case where the recording speed is heightened.

What is claimed is:
 1. An information recording apparatus in which alaser light is irradiated onto a recording medium and a recording markcorresponding to a recording signal is formed, said informationrecording apparatus comprising: a light source to emit the laser light;and a controller which controls to irradiate a laser pulse onto therecording medium when said light source is driven according to therecording signal, wherein said controller includes; a mark controller bywhich, during a mark-period of the recording signal, an output level ofthe laser pulse is changed corresponding to the recording signal betweena normal level and a writing level higher than the normal level; and aspace controller by which, during at least several space periods in therecording signal, the output level of the laser pulse is changed to alow level lower than the normal level covering over a predeterminedperiod.
 2. The information recording apparatus according to claim 1,wherein the low level lower than the normal level is zero level.
 3. Theinformation recording apparatus according to claim 1, wherein said spacecontroller changes the output level of the laser pulse to the low levellower than the normal level only in the space period in which the timewidth is short.
 4. The information recording apparatus according toclaim 3, wherein the space period in which the time width is short is aspace period of 3T or 4T.
 5. The information recording apparatusaccording to claim 1, wherein said space controller changes the outputlevel of the laser pulse to the low level lower than the normal level inall space periods.
 6. The information recording apparatus according toclaim 1, wherein in the space period in which the time width is long,said space controller changes the output level of the laser pulse to thelow level covering over the predetermined first period, and in the spaceperiod in which the time width is short, said space controller changesthe output level of the laser pulse to the low level covering over thesecond period longer than the fist period.
 7. The information recordingapparatus according to claim 6, wherein the space period in which thetime width is short is a space period of 3T or 4T, and the space periodin which the time width is long is a space period of 5T or more.
 8. Theinformation recording apparatus according to claim 1, furthercomprising: a level adjuster which automatically adjusts the outputlevel of the laser pulse covering over the level adjustment period inthe predetermined space period, wherein said space controller changesthe output level of the laser pulse to the low level lower than thenormal level only in the space period in which the automatic adjustmentof the output level is not conducted.
 9. The information recordingapparatus according to claim 1, further comprising: a level adjusterwhich automatically adjusts the output level of the laser pulse coveringover the level adjustment period in the predetermined space period,wherein said space controller changes the output level of the laserpulse to the low level lower than the normal level in the period exceptthe level adjustment period in all space periods.
 10. The informationrecording apparatus according to claim 1, further comprising: a leveladjuster which automatically adjusts the output level of the laser pulsecovering over the level adjustment period in the predetermined spaceperiod, wherein in the space period in which the automatic adjustment ofthe output level is conducted, said space controller changes the outputlevel of the laser pulse to the low level covering over thepredetermined first period which is not overlapped with the leveladjustment period, and in the space period in which the automaticadjustment of the output level is not conducted, said space controllerchanges the output level of the laser pulse to the low level coveringover the second period which is longer than the first period.
 11. Theinformation recording apparatus according to claim 1, wherein therecording medium can records only once, and the normal level is thereading level.
 12. The information recording apparatus according toclaim 1, wherein the recording medium can write or erase for a pluralityof times, and the normal level is an erasing level.
 13. The informationrecording apparatus according to claim 1, wherein said space controllerchanges the output level of the laser pulse to the low level lower thanthe normal level from the top of the space period.
 14. An informationrecording method in which the laser light is irradiated onto a recordingmedium and a recording mark corresponding to a recording signal isformed, said information recording method comprising the steps of:emitting a laser light; and irradiating a laser pulse onto the recordingmedium by driving a light source according to the recording signal,wherein the step of irradiating the laser pulse includes the steps of;during a mark period of the recording signal, changing an output levelof the laser pulse between a normal level and a writing level higherthan the normal level, corresponding to the recording signal, and duringat least several space periods of the recording signal, changing theoutput level of the laser pulse to a low level lower than the normallevel covering over a predetermined period.